Fuel injection valve for high-pressure fuel injection

ABSTRACT

An improved fuel injection valve for a high-pressure injection of fuel from a central high-pressure line into combustion chambers of an internal combustion engine, which has an injection valve with a valve seat, a valve ball, and a guide piece that guides the valve ball. The guide piece presses the valve ball against the valve seat in order to close the injection control valve and during the opening, subjects the valve ball to an initial stress of a spring. During the opening, the valve ball is lifted up from the valve seat by means of a high-pressure jet which is supplied via an outlet throttle bore by a control chamber that is operatively connected with a central high-pressure line. A diffuser is disposed between the valve seat and the outlet throttle bore, and the outlet throttle bore, the diffuser, and the valve seat have the approximate shape of a steep-walled funnel with a right-angled to acute-angled cone angle.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to fuel injection valves, and more particulary toa fuel injection; valve for a high-pressure injection.

2. Description of the Prior Art

An injection valve of the type with which this invention is concernedhas been disclosed in European patent application 0 661 442 A1. Fuelinjection valves of this kind have a control chamber which, by means ofan inlet throttle bore, continuously communicates with a high-pressurefuel source by way of a high-pressure line. A valve closing member ofthe fuel injection valve is kept in the closed position as long as thecontrol pressure prevailing in the control chamber is high.

The control chamber can be discharged by means of an outlet throttlebore which is acted upon by an injection control valve. As soon as theinjection control valve opens the outlet throttle bore, the controlchamber is discharged and the valve closing member of the fuel injectionvalve switches into its open position so that the injection into acombustion chamber of an internal combustion engine can take place. Whenthe injection control valve closes the outlet throttle bore again, thevalve closing member is brought back into the closed position as aresult of the pressure increase in the control chamber.

Speed, precision, and reproducibility of the opening and closingmovements of the injection control valve are of crucial importance forthe quality of the fuel injection. The reproducibility of the openingand closing movements is decisively determined by the design of theinjection control valve that is essentially a valve seat that in orderto open and close the outlet throttle bore, cooperates with a valve ballthat is pressed against the valve seat by a guide piece in order toclose and open the injection control valve or is subjected to an initialstress of a spring in order to open it.

A recess in the guide piece that guides the valve ball is in factadapted to the diameter of the valve ball, but radial displacements ofthe ball in relation to the ball seat can occur if the high-pressure jetat the outlet throttle bore strikes the valve ball in a radially offsetmanner. Furthermore transient effects can occur until the ball is liftedup centrally from the valve seat and finally, the embodiment of thevalve seat as a flat cone does not assure that the valve ball will closethe valve seat without radial displacement and without the occurrence oftransient effects during the closing process.

FIG. 3 shows a detail of a typical embodiment of the essentialconstructive parts of an injection control valve. By means of thecrimped screw connection 11, the fuel injection valve is connected tothe central high-pressure line 6 which in turn communicates with ahigh-pressure fuel source. By means of an inlet throttle bore 10, acontrol chamber 7 is placed under high-pressure which acts on a valveclosing member 12 that keeps the fuel injection valve closed as long asthe high pressure prevails in the high-pressure control chamber. Bymeans of a discharge bore that transitions into an outlet throttle bore8, the control chamber 7 can be discharged so that the valve closingmember opens the fuel injection valve and fuel from the centralhigh-pressure line 6 is injected into the combustion chambers of aninternal combustion engine. The opening and closing of the outletthrottle bore 8 is assured by means of an injection control valve thathas a valve seat 2, a valve ball 3, and a guide piece 4 that guides thevalve ball 3. The flat cone-shaped valve seat with an obtuse openingangle α can also be clearly seen here, which has also been disclosed bythe reference EP 0 661 442 A1 in FIG. 2.

Each occurrence of transient effects and/or of radial displacements ofthe valve ball in relation to the center of the centrally disposedoutlet throttle bore reduces the precision and reproducibility of theopening and closing movements of the injection control valve.

The object of the invention, therefore, is to overcome the disadvantagesof fuel injection valves of the prior art, to assure a reliable, uniformclosing of the valve ball in the injection control valve, and to reducedistortions due to transient effects or other obstructions to the valveball during the closing of the injection control valve.

SUMMARY OF THE INVENTION

The disposition of a diffuser between the valve seat and the outletthrottle bore advantageously achieves the fact that compared to theembodiment according to EP 0 661 442 A1, a higher percentage of thekinetic energy of the high-pressure jet emerging from the throttle boreis converted into static pressure. Consequently, due to the greateraverage diameter of the diffuser in relation to the throttle bore, thepressure contacts a greater service area of the valve ball as it isopening. Consequently, the valve ball is uniformly and reproduciblycentered as it is lifting up and radial displacements of the valve ballin relation to the outlet throttle bore can be prevented to the greatestextent possible.

The embodiment approximately in the shape of a steep-walled funnelcomposed of the outlet throttle bore, diffuser, and valve seat, in whichthe funnel shape has a right-angled to acute-angled cone angle a,advantageously achieves the fact that in contrast to the conventionalvalve seat composed of a flat cone with an outlet throttle bore disposedcentrally at the tip of the cone, the funnel wall of the valve seatencourages the centering of the valve ball during the closing of theinjection control valve and prevents a radial displacement of the valveball in relation to the diffuser and the outlet throttle bore.Consequently, the embodiment according to the invention of the injectioncontrol valve in the fuel injection valve achieves an increasedprecision and reproducibility of the opening and closing movement.

Usually, the diffuser is a constant widening from a minimal diameter toa maximal diameter. In this connection, increasingly and steadily, thekinetic energy of a flowing medium is partially converted into staticpressure. In a preferred embodiment of the invention, the diffuser isembodied as a “cross sectional jump”, i.e. the minimal and maximaldiameter of the diffuser are equal. This represents an inconstantwidening of the outlet throttle bore to the diameter of the diffuser,which is normally referred to as a Carnot opening. A Carnot opening ofthis kind has the advantage that the resistance coefficient æ can beoptimized by means of simply changing the ratio between the diameter ofthe diffuser and the diameter of the outlet throttle bore.

In a preferred embodiment of the invention, the ratio between theaverage diameter of the diffuser and the diameter of the outlet throttlebore lies between 1.2 and 2 so that the resistance coefficient æ can beset between about 0.16 and about 9.

In another preferred embodiment of the invention, the cone angle æ is60° to 90°. In contrast to the flat cone known from the prior art, thissteep-walled cone permits an improved centering of the valve ball. Withcone angles of greater than 60°, the centering of the valve ball is infact more strongly encouraged, but the ball cannot protrude into thediffuser far enough to be suspended as close as possible to the outletthrottle bore when the injection control valve is closed. On the otherhand, with cone anglesα of greater than 90°, the centering action of thefunnel shape becomes increasingly less effective so that there is anincrease in the disadvantages explained above for the prior art.

Preferably, the valve ball protrudes with between ⅕ and {fraction(1/10)} of its radius r into the diffuser. This can advantageouslyresult in the fact that on the one hand, a sufficiently large sphericalcap of the valve ball is struck by the high-pressure jet and lifted upfrom the valve seat in a centered fashion and on the other hand, thevalve ball is prevented from protruding too far into the diffuser.

In another embodiment of the invention, the maximal diameter D of thediffuser and the length 1 of the diffuser are matched to one another insuch a way that when the injection valve is closed, the valve ball ispositioned at a distance of ≦0.1 mm, preferably between 30 and 80 μm,above the outlet throttle bore. This spacing preferably assures thatduring the opening of the injection control valve, not only does thehigh-pressure jet from the outlet throttle bore initially act on thevalve ball surface in the vicinity of the throttle bore, but also thepressure acts on the larger surface area of a spherical cap of the valveball in the vicinity of the maximal diameter of the diffuser or of thevalve seat.

The length-to-diameter ratio of the outlet throttle bore is crucial forthe percentage of the throttling action. The smaller the diameter andthe greater the length of the throttle bore, the more intense thethrottling action is. Increasing throttling action also results in areduced consumption of the fuel emerging from the control chamber. Atthe same time, however, the time required to decrease the high pressurein the control chamber increases. Therefore, the range from 1 to 20 forthe length-to-diameter ratio of the outlet throttle bore represents anoptimal compromise between these two extremes.

Furthermore, the diffuser preferably has a length-to-maximal diameterratio between 0.1 and 0.5. This length-to-maximal diameter ratio of thediffuser results in the fact that the flow does not come into contactwith the casing-shaped wall of the diffuser so that the frictionallosses in the diffuser become negligibly small while the flow lossesincrease due to turbulence generation at the step-shaped transition.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages, features, and potential applications of the currentinvention will be apparent from the following description taken inconnection with the drawings, in which;

FIG. 1 shows a cross-section through a fuel injection valve in thevicinity of a valve seat of an injection control valve in a firstembodiment of the invention;

FIG. 2 shows a cross section through a fuel injection valve in thevicinity of a valve seat of an injection control valve in a secondembodiment of the invention; and

FIG. 3 shows a detailed cross section the vicinity of the essentialstructural parts of a conventional injection control valve.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings in detail,

FIG. 1 shows a cross section through a fuel injection valve in thevicinity of a valve seat 2 of an injection control valve in a firstembodiment of the invention. A pressure chamber 7 communicates with acentral high-pressure line 6 by means of an inlet throttle bore 10 shownin FIG. 3 and is therefore subjected to a fuel pressure between 150 and300 MPa. A discharge bore 13, which transitions into an outlet throttlebore 8, can be used to discharge the control chamber 7 when the valveball 3 of the injection control valve lifts up from the valve seat 2 inthe arrow direction A counter to an initial stress of a spring 5.

During opening and closing, the valve ball 3 is secured by a guide piece4 shown in FIG. 3, which guides the valve ball 3. The centering of theball 3 in relation to the valve seat 2 is essentially assured by meansof a steep-walled funnel shape which has a right-angled to acute-angledcone angle α, which is 90° in this preferred embodiment. As a result,the high-pressure jet from the outlet throttle bore 8 can advantageouslystrike the valve ball 3 centrally and can lift it up in the arrowdirection A as soon as a solenoid valve relieves the valve ball 3 from apressure against the valve seat 2. A diffuser 9 is disposed between thevalve seat 2 and the outlet throttle bore 8 and in this embodiment, theminimal diameter d and the maximal diameter D of the diffuser 9 areequal.

In this embodiment, the length-to-diameter ratio of the diffuser 9 is0.2 and the length-to-diameter ratio of the outlet throttle bore 8 is<2. The valve ball 3 protrudes with an eighth of its radius r into thediffuser 9 and when the injection control valve is closed, is positionedat a distance of 80 μm above the throttle bore. The cross-sectionalwidening between the outlet throttle bore and diffuser 9 constitutes aCarnot opening in which the flow of the high-pressure jet, which isdirected from the outlet throttle bore 8 toward the center of the valveball 3, no longer contacts the walls of the diffuser 9 in a laminarfashion, but produces loss-encumbered flow turbulence at thecross-sectional widening.

Despite these flow losses, the diffuser 9, in connection with thesteep-walled valve seat 2, has a significantly greater centering actionon the valve ball 3 than the onventional flat cone-shaped valve seat inconnection with an immediate transition from the outlet throttle bore 8to the valve seat 2 in the prior art.

FIG. 2 shows a cross section through the fuel injection valve in thevicinity of the valve seat of the injection control valve in a secondembodiment of the invention. As is apparent in this embodiment, the coneangle α is significantly more acute than in the first embodimentaccording to FIG. 1. In this instance, the cone angle α=60° and thelength-to-diameter ratio of the diffuser is 0.15.

In this exemplary embodiment, the valve ball 3 protrudes significantlyfurther into the diffuser 9 and when the injection control valve isclosed, is suspended 30 μm above the outlet rim 14 of the outletthrottle bore 8. This acute-angled cone of the valve seat 2 centers thevalve ball 3 hydraulically. This means that the closing can take placein a frictionless manner and distortions in the return quantity do notoccur during the closing of the valve ball 3. The extremely shortdiffuser bore with a length-to-diameter ratio of 0.15 permits thehigh-pressure jet emerging from the outlet throttle bore 8 to strike theball not significantly outside the center line 15. This results infurther reduced radial forces. Furthermore, the relatively largediffuser bore has the advantage that the steep-walled valve seat 2 canbe better machined and polished.

FIG. 3 shows a detailed cross section the vicinity of the essentialstructural parts of the conventional injection control valve asextensively described above in the prior art section.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

I claim:
 1. A fuel injection valve for a high-pressure injection of fuelfrom a central high-pressure line (6) into combustion chambers of aninternal combustion engine, including an injection valve (1) with avalve seat (2), a valve ball (3), and a guide piece (4) that guides thevalve ball (3), which guide piece presses the valve ball (3) against thevalve seat (2) in order to close the valve and, in order to open thevalve, subjects the valve ball (3) to an initial stress of a spring (5),and in the open state, permits the valve ball (3) to be lifted up fromthe valve seat (2) by means of a high-pressure jet which is supplied viaan outlet throttle bore (8) by a control chamber (7) that communicateswith a central high-pressure line (6), the improvement comprising adiffuser (9) disposed between the valve seat (2) and the outlet throttlebore (8), said outlet throttle bore (8), said diffuser (9), and saidvalve seat (2) having the approximate shape of a steep-walled funnelwith a right-angled to acute-angled cone angle (α).
 2. The fuelinjection valve according to claim 1, wherein the minimal diameter (d)and the maximal diameter (D) of the diffuser (9) are equal.
 3. The fuelinjection valve according to claim 1, wherein the ratio between anaverage diameter d_(m) of the diffuser (9) and a diameter (m) of theoutlet throttle bore (8) lies between 1.2 and
 2. 4. The fuel injectionvalve according to claim 1, wherein the cone angle (α) is within therange about 60 to 90°.
 5. The fuel injection valve according to claim 1,wherein the valve ball (3) protrudes with between ⅕ and {fraction(1/10)} of its radius (r) into the diffuser (9).
 6. The fuel injectionvalve according to claim 1, wherein the maximal diameter (D) of thediffuser (9) and the length of the diffuser (9) are matched to oneanother in such a way that when the injection valve (1) is closed, thevalve ball (3) is positioned at a distance of ≦0.1 mm.
 7. The fuelinjection valve according to claim 6, wherein the valve ball (3) ispositioned at a distance of between 30 and 80 μm, above the outletthrottle bore (8).
 8. The fuel injection valve according to claim 1,wherein outlet throttle bore has a length-to-diameter ratio between 1and
 20. 9. The fuel injection valve according to claim 1, wherein thediffuser (9) has a length-to-maximal diameter ratio between 0.1 and 0.5.10. The fuel injection valve according to claim 2, wherein the ratiobetween an average diameter d_(m) of the diffuser (9) and a diameter (m)of the outlet throttle bore (8) lies between 1.2 and
 2. 11. The fuelinjection valve according to claim 10, wherein the cone angle (α) iswithin the range about 60 to
 900. 12. The fuel injection valve accordingto claim 11, wherein the valve ball (3) protrudes with between ⅕ and{fraction (1/10)} of its radius (r) into the diffuser (9).
 13. The fuelinjection valve according to claim 11, wherein the maximal diameter (D)of the diffuser (9) and the length of the diffuser (9) are matched toone another in such a way that when the injection valve (1) is closed,the valve ball (3) is positioned at a distance of ≦0.1 mm.
 14. The fuelinjection valve according to claim 12, wherein the valve ball (3) ispositioned at a distance of between 30 and 80 μm, above the outletthrottle bore (8).
 15. The fuel injection valve according to claim 14,wherein outlet throttle bore has a length-to-diameter ratio between 1and
 20. 16. The fuel injection valve according to claim 15, wherein thediffuser (9) has a length-to-maximal diameter ratio between 0.1 and 0.5.17. The fuel injection valve according to claim 2, wherein the coneangle (α) is in the range about 60 to 90°.
 18. The fuel injection valveaccording to claim 3, wherein the maximal diameter (D) he diffuser (9)and the length of the diffuser (9) are matched to one another in h a waythat when the injection valve (1) is closed, the valve ball (3) ispositioned distance of ≦0.1 mm.
 19. The fuel injection valve accordingto claim 18, wherein outlet throttle bore has a length-to-diameter ratiobetween 1 and
 20. 20. The fuel injection valve according to claim 19,wherein the diffuser (9) has a length-to-maximal diameter ratio between0.1 and 0.5.